assignment_to_function

Functions can't be assigned a value.

The analyzer produces this diagnostic when the name of a function appears on the left-hand side of an assignment expression.

The following code produces this diagnostic because the assignment to the function f is invalid:

void f() {}

void g() {
  f = () {};
}

If the right-hand side should be assigned to something else, such as a local variable, then change the left-hand side:

void f() {}

void g() {
  var x = () {};
  print(x);
}

If the intent is to change the implementation of the function, then define a function-valued variable instead of a function:

void Function() f = () {};

void g() {
  f = () {};
}